Blade tip profile

ABSTRACT

An airfoil includes a blade having a leading edge, a trailing edge, a pressure side, a suction side, a tip, and a scoop. The scoop extends along the tip of the blade. The scoop comprises a difference in a radial height of the blade from a pressure side to a suction side of the blade. The radial height of the blade at the pressure side is less than the radial height of the blade at the suction side.

BACKGROUND

A gas turbine engine is a rotating device that uses the action of a fluid to produce work. In a gas turbine engine, a pressurized, high temperature gas is the driving force. One of the reasons that gas turbine engines are widely used to power aircraft is they are light and compact and have a high power-to-weight ratio.

Gas turbine engines typically include several stages including a fan, a compressor, a combustor, and a turbine. Some of these stages utilize rotating airfoils with shaped blades arranged in series. The blades convert energy from combustion gases produced by the combustor into mechanical work used to turn a rotor. The blades positioned forward of the combustor are turned by the rotor to compress air entering the combustor.

Blades usually have a clearance gap between the blade tip and the stationary casing or the shroud surface adjacent the blade tip. This clearance gap is typically called a tip gap. This clearance gap is necessary to allow for rotation of the blade and to allow for mechanical and thermal growth of the blade. Due to the pressure difference between the pressure side and the suction side of the blade, hot gas leaks across this gap from the pressure side to the suction side. This phenomenon is known as tip leakage flow.

The tip leakage flow results in a reduction in the blade force, (e.g., the work done) and therefore, the overall efficiency of the gas turbine engine. In fact, the losses that are attributed to leakage flow can be very substantial. Leakage flow also increases the thermal loading on the blade tip, leading to high local temperatures adjacent the tip, and thus, is considered one of the primary sources of blade failure. Typically, leakage flow is reduced by using a recessed or squealer tip blade or by modifying the blade tip to incorporate film cooling.

Blades, including turbine blades in particular, can utilize a pocket recess which comprises a recess cavity that extends radially through the length of the blade. The pocket recess creates an opening at the tip of the blade. The pocket recess is used for efficiency purposes to reduce the weight of the blade and to reduce blade creep. However, due to excessive blade tip leakage, the efficiency of the pocket recess is limited.

SUMMARY

An airfoil includes, a blade having a leading edge, a trailing edge, a pressure side, a suction side, a tip, and a scoop. The scoop extends along the tip of the blade. The scoop comprises a difference in a radial height of the blade from a pressure side to a suction side of the blade. The radial height of the blade at the pressure side is less than the radial height of the blade at the suction side.

In another aspect, a blade includes an outer radial surface disposed along a suction side of a tip of the blade, an inner radial surface disposed along a pressure side of the tip of the blade, and a pocket recess. The inner radial surface has a different radial height than the outer radial surface. The pocket recess is open at the tip of the blade and is disposed between the inner radial surface and the outer radial surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of an airfoil including a blade tip scoop and a pocket recess.

FIGS. 2A and 2B are perspective views of the airfoil of FIG. 1.

FIGS. 3A and 3B are perspective views of a second embodiment of an airfoil including a blade tip scoop and a pocket recess.

FIGS. 4A and 4B are perspective views of a third embodiment of an airfoil including a blade tip scoop and a pocket recess.

FIGS. 5A and 5B are perspective views of a fourth embodiment of an airfoil including a blade tip scoop and a pocket recess.

DETAILED DESCRIPTION

FIG. 1 shows a first embodiment of an airfoil 8A for a gas turbine engine including a blade 10A, a blade tip 12A, and a pocket recess 14A disposed along a camber line 16A of blade 10A. Blade 10A includes a leading edge 18A, a trailing edge 20A, a pressure surface 22A, and a suction surface 24A. Blade 10A additionally includes a scoop 26A disposed along blade tip 12A. Due to scoop 26A, blade tip 12A includes an outer radial surface 28A and an inner radial surface 30A. During operation, when mounted on a rotor (not shown), airfoil 8A would rotate in the direction D illustrated to work air A flowing past airfoil 8A, as shown in FIG. 2A. During such operation, tip leakage T_(L) would occur. Scoop 26A would generate a rotational vortex V (FIGS. 2A and 2B) that would rotate in an opposing direction to the direction D of rotation of airfoil 8A and in an opposing direction to the direction of tip leakage T_(L). This counter rotating vortex V reduces tip leakage T_(L), and thereby improves the efficiency of the airfoil 8A and gas turbine engine.

Airfoil 8A is of conventional design and includes a blade 10A extending generally radially outward from a platform section (not numbered) and a root section (not numbered) to blade tip 12A. When installed, blade tip 12A is disposed adjacent gas turbine engine stator case (not shown). Pocket recess 14A extends into blade 10A at blade tip 12A. In the embodiment shown in FIGS. 1, 2A, and 2B, pocket recess 14A is symmetric with respect to camber line 16A of blade 10A. Thus, pocket recess 14A straddles and is bifurcated by camber line 16A, is disposed adjacent leading edge 18A in a thicker region of blade 10A, and is substantially equidistant from pressure surface 22A and suction surface 24A of blade 10A.

Blade 10A extends from leading edge 18A along concave pressure surface 22A and along convex suction surface 24A to trailing edge 20A. For reference purposes, camber line 16A extends along blade tip 12A from leading edge 18A to trailing edge 20A. Pocket recess 14A is separated from exterior of blade 10A and pressure surface 22A by first wall 32A. Similarly, pocket recess 14A is separated from exterior of blade 10A and suction surface 24A by second wall 34A. Because pocket recess 14A is symmetric with respect to camber line 16A, first wall 32A has substantially a same thickness as second wall 34A along a corresponding extent of pocket recess 14A.

Scoop 26A extends along blade tip 12A from leading edge 18A to trailing edge 20A. Thus, in the embodiment shown both outer radial surface 28A and inner radial surface 30A of blade tip 12A extend from leading edge 18A to trailing edge 20A. Scoop 26A comprises a cutout along a pressure side of blade 10A. Thus, scoop 26A forms step feature that extends along blade tip 12A. In the embodiment shown, the step or change in radial height H in blade 10A between outer radial surface 28A and inner radial surface 30A is generally aligned on camber line 16A. Outer radial surface 28A extends along a suction side of blade tip 12A and inner radial surface 30A extends along a pressure side of blade tip 12A.

Because the construction and operation of gas turbine engines is known in the art, gas turbine engine will not be discussed in great detail. While blade 10A is shown as a separate component removable from a rotor (not shown) in other embodiments airfoil can be integrated with the rotor. Although described with reference to a turbine airfoil, in other embodiments blade can be utilized in the compressor or other stage of the gas turbine engine.

Consider an incompressible inviscid turbine tip clearance flow field; the flow through the tip gap is obtained from Bernoulli equation is as shown in Equation 1:

$\begin{matrix} {W_{L} = \sqrt{2\frac{P_{p} - P_{s}}{\rho}}} & (1) \end{matrix}$

Where Pp=Pressure side pressure, Ps=Suction side pressure, ρ=. Gas density, and W_(L)=Leakage flow.

As shown in FIGS. 2A and 2B, leakage flow W_(L) is reduced if a tip vortex V is generated at the blade tip in the opposite direction to tip leakage flow T_(L) and in the opposite direction to blade 10A rotation. The rolling up of the counter rotation of tip vortex V is due to scoop 26A with step from pressure to suction side of blade tip 12A. Additionally, vortex creation is enhanced by pocket recess 14A. Results regarding vortex creation can be verified and analyzed utilizing commercially available computational fluid dynamics software.

As previously discussed, creation of counter rotating vortex V at blade tip 12A leads to a reduction in blade tip leakage T_(L), which results in improved gas turbine engine efficiency and fuel savings. Operating temperatures within the turbine engine can be increased as a result of decreased temperature localization, which results in reduced emissions. Additionally, reduced blade tip leakage T_(L) results in extended hot section durability due to a reduction in the thermal loading on the blade tip 12A. In instances of disc-blade coupling mistuning, a turbine wheel with tip modification as described would result in tuning out the interfered frequency and also aids in maintaining a balanced rotor.

FIGS. 2A and 2B provide additional perspective views of blade 10A with scoop 26A. As discussed previously, the radial height. H of blade 10A differs between outer radial surface 28A and inner radial surface 30A. Scoop 26A has a fillet radius R along radial height H between outer radial surface 28A and inner radial surface 30A. In the embodiments shown in FIGS. 2A and 2B, scoop 26A additionally includes an aft length L₁ and a forward length L₂ along the step transition between outer radial surface 28A and inner radial surface 30A. Outer radial surface 28A has a thickness T₁ along camber line 16A that is substantially the same as a corresponding thickness T₂ of inner radial surface 30A (T₁≈T₂).

Scoop 26A comprises a curved step between outer radial surface 28A and inner radial surface 30A and extends the entire length of blade tip 12A from leading edge 18A to trailing edge 20A. Radial height H between outer radial surface 28A and inner radial surface 30A will vary from embodiment to embodiment. In one embodiment, the radial height H is greater than or equal to the tip clearance (the distance between the stator casing and the outermost radial extent of blade tip 12A) and is less than or equal to about 15% of the blade span. Radius R is greater than or equal to height H. Aft length L₁ and a forward length L₂ along step feature between outer radial surface 28A and inner radial surface 30A will vary from embodiment to embodiment and vary as a function of pocket axial length, pocket configuration, and step lateral thickness (expressed in term of T₁ and T₂).

FIGS. 3A and 3B show a second embodiment of an airfoil 8B for a gas turbine engine including a blade 10B, a blade tip 12B, a pocket recess 14B, and a camber line 16B of blade 10B. Blade 10B includes a leading edge 18B, a trailing edge 20B, a pressure surface 22B, and a suction surface 24B. Blade 10B additionally includes a scoop 26B disposed along blade tip 12B. Due to scoop 26B, blade tip 12B includes an outer radial surface 28B and an inner radial surface 30B. During operation when mounted on a rotor (not shown) airfoil 8B would rotate in the direction D illustrated. During such operation, tip leakage T_(L) would occur. Scoop 26B generates a rotational vortex V that would rotate in an opposing direction to the direction D of rotation of airfoil 8B and in an opposing direction to the direction of tip leakage T_(L). This counter rotating vortex V would reduce tip leakage T_(L), and thereby, improve the efficiency of the airfoil 8B and gas turbine engine.

Pocket recess 14B extends into blade 10B from blade tip 12B. In the embodiment shown in FIGS. 3A and 3B, pocket recess 14B is asymmetric with respect to camber line 16B of blade 10B. Thus, a first wall 32B of the blade 10B has a thickness that differs from a corresponding thickness of second wall 34B at a substantially similar location with respect to camber line 16B. Pocket recess 14B is biased toward the pressure side of camber line 16B leaving first wall 32B a thinner thickness than second wall 34B along a corresponding extent of pocket recess 14B.

For reference purposes, camber line 16B extends along blade tip 12B from leading edge 18B to trailing edge 20B. Blade 10B extends from leading edge 18B along concave pressure surface 22B and along convex suction surface 24B to trailing edge 20B. Scoop 26B is biased away from camber line 16B toward pressure side. Scoop 26B extends along blade tip 12B from leading edge 18B and trailing edge 20B. Thus, in the embodiment shown inner radial surface 30B and outer radial surface 28B of blade tip 12B extend from leading edge 18B to trailing edge 20B. Scoop 26A comprises a cutout or step feature that extends along blade tip 12B.

Due to the changes in the configuration of scoop 26B and pocket recess 14B compared to the embodiments of FIGS. 2A and 2B, lateral thickness T₁ of outer radial surface 28B along camber line 16B greater than corresponding lateral thickness T₂ of inner radial surface 30A.

FIGS. 4A and 4B show a third embodiment of an airfoil 8C for a gas turbine engine including a blade 10C, a blade tip 12C, a pocket recess 14C, and a camber line 16C of blade 10C. Blade 10C includes a leading edge 18C, a trailing edge 20C, a pressure surface 22C, and a suction surface 24C. Blade 10C additionally includes a scoop 26C disposed along blade tip 12C. Due to scoop 26C, blade tip 12C includes an outer radial surface 28C and an inner radial surface 30C. During operation when mounted on a rotor (not shown) airfoil 8C would rotate in the direction D illustrated. During such operation, tip leakage T_(L) would occur. Scoop 26C generates a rotational vortex V that would rotate in an opposing direction to the direction D of rotation of airfoil 8C and in an opposing direction to the direction of tip leakage T_(L). This counter rotating vortex V would reduce tip leakage T_(L), and thereby, improve the efficiency of the airfoil 8C and gas turbine engine.

Pocket recess 14C extends into blade 10C from blade tip 12C. In the embodiment shown in FIGS. 4A and 4B, pocket recess 14C is asymmetric with respect to camber line 16C of blade 10C. Thus, a first wall 32C of the blade 10C has a thickness that differs from a corresponding thickness of second wall 34C at a substantially similar location with respect to camber line 16C. Pocket recess 14C is biased toward the suction side of camber line 16C leaving first wall 32C a thicker thickness than second wall 34C along a corresponding extent of pocket recess 14C.

Blade 10C extends from leading edge 18C along concave pressure surface 22C and along convex suction surface 24C to trailing edge 20C. For reference purposes, camber line 16C extends along blade tip 12C from leading edge 18C to trailing edge 20C. Step between outer radial surface 28C and inner radial surface 30C runs along and straddles camber line 16C. Scoop 26C is of a reduced size and is offset from camber line 16C. Thus, scoop 26C is asymmetric with respect to camber line 16C. Therefore, outer radial surface 28C has a lateral thickness T₁ along camber line 16C that differs from a corresponding lateral thickness T₂ of inner radial surface 30C (T₁<T₂) and scoop 26C extends from leading edge 18C to trailing edge 20C. Due to the changes in position of pocket cavity 14C compared to the embodiments of FIGS. 1, 2A, 2B, 3A, and 3B aft length L₁ and forward length L₂ sections differ in extent.

FIGS. 5A and 5B show a fourth embodiment of an airfoil 8D for a gas turbine engine including a blade 10D, a blade tip 12D, a pocket recess 14D, and a camber line 16D of blade 10D. Blade 10D includes a leading edge 18D, a trailing edge 20D, a pressure surface 22D, and a suction surface 24D. Blade 10D additionally includes a scoop 26D disposed along blade tip 12D. Due to scoop 26D, blade tip 12D includes an outer radial surface 28D and an inner radial surface 30D. During operation when mounted on a rotor (not shown) airfoil 8D would rotate in the direction D illustrated. During such operation, tip leakage T_(L) would occur. Scoop 26D generates a rotational vortex V that would rotate in an opposing direction to the direction D of rotation of airfoil 8D and in an opposing direction to the direction of tip leakage T_(L). This counter rotating vortex V would reduce tip leakage T_(L), and thereby, improve the efficiency of the airfoil 8D and gas turbine engine.

Pocket recess 14D extends into blade 10D from blade tip 12D. In the embodiment shown in FIGS. 5A and 5B, pocket recess 14D is asymmetric with respect to camber line 16D of blade 10D. Pocket recess 14D is disposed such that pocket recess 14D is angled with respect to camber line 16D. Because pocket recess 14D is disposed asymmetrically with respect to camber line 16D, first wall 32D of the blade 10D has increasing thickness along the axial length of pocket recess 14D from forward to aft and second wall 34D with a decreasing thickness along the axial length of pocket recess 14D. First wall 32D has a lesser thickness adjacent leading edge 18D than aft near a trailing termination edge of pocket recess 14D. Similarly, a corresponding thickness of second wall 34D is greater near the leading edge 18D and decreases in thickness with travel aft along pocket recess 14D. Thus, second wall 34D has decreasing thickness along the length of pocket recess 14D from forward to aft.

Scoop 26D is disposed asymmetrically with respect to camber line 16D such that step feature does not straddle or follow camber line 16D. Rather, outer radial surface 28D has a thickness T₁ along camber line 16D that differs from a corresponding thickness T₂ of inner radial surface 30D. During aft length L₁ of scoop 26D outer radial surface 28D thickness T₁ is less than corresponding thickness T₂ of inner radial surface 30D. During forward length L₂ of scoop 26D, outer radial surface 28D thickness T₁ is greater than corresponding thickness T₂ of inner radial surface 30D.

An asymmetric pocket cavity such as pocket cavities 14B, 14C, and 14D alters the mass/stiffness of the blade 10B, 10C, and 10D, thereby shifting or tuning away the natural frequency of the pocket cavity and blade from the frequency of acoustic pressure oscillation or the frequency of the aero-excitation source.

More particularly, blade can be tuned at blade anti-nodes as further discussed in United States Patent Application Publications 2010/0278632A and 2010/0278633A, which are incorporated herein by reference. Tuning is performed by modifying the stiffness/mass (i.e. wall thickness) at one or more blade anti-nodes. Increasing the mass at the blade anti-node decreases natural frequency, and decreasing mass at blade anti-node increases natural frequency. Wall thickness as a result of pocket recess geometry can be modified until the natural frequency of the blade resonant mode shapes that have interferences are moved out of the expected acoustic pressure oscillation frequency or out of the aero-excitation source frequency. Wall thickness as a result of the pocket recess geometry can be further modified to further increase a substantially resonance-free running range. If further tuning is desired, the pocket recess geometry can be modified on one or more additional blade anti-nodes until the blade has no natural frequencies that excite at the expected acoustic pressure oscillation frequency or aero-excitation frequency. The natural frequency of the blade resonant mode shapes can be modeled using a finite element method.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. An airfoil comprising: a blade having a leading edge, a trailing edge, a pressure side, a suction side, and a tip; and a scoop extending along the tip of the blade, wherein the scoop comprises a difference in a radial height of the blade from the pressure side to the suction side of the blade, and wherein the radial height of the blade at the pressure side is less than the radial height of the blade at the suction side.
 2. The airfoil of claim 1, further comprising a pocket recess opening at a tip of the blade.
 3. The airfoil of claim 2, wherein the pocket recess is asymmetric with respect to a camber line of the blade.
 4. The airfoil of claim 2, wherein the pocket recess is biased toward one of a suction side or a pressure side of the blade.
 5. The airfoil of claim 2, wherein the pocket recess is angled with respect to a camber line of the blade such that a first wall of the blade is thicker adjacent the leading edge than a second wall of the blade.
 6. The airfoil of claim 1, wherein the scoop extends from the leading edge to the trailing edge of the blade.
 7. The airfoil of claim 1, wherein the difference in radial height between the pressure side and the suction side is greater than or equal to tip clearance and is less than or equal to about 15% of blade span.
 8. The airfoil of claim 1, wherein the scoop has a step feature at the tip of the blade, and wherein the step feature comprises a change in radial height between an outer radial surface and an inner radial surface of the tip of the blade.
 9. The airfoil of claim 8, wherein the step feature has a fillet radius.
 10. The airfoil of claim 8, wherein the step feature extends along a camber line of the blade such that the outer radial surface has substantially a same thickness as the inner radial surface.
 11. The airfoil of claim 8, wherein the step feature is asymmetric with respect to a camber line of the blade.
 12. The airfoil of claim 11, wherein the step feature is biased toward one of the suction side or the pressure side.
 13. The airfoil of claim 11, wherein the step feature is angled with respect to the camber line.
 14. A blade comprising: an outer radial surface disposed along a suction side of a tip of the blade; an inner radial surface disposed along a pressure side of the tip of the blade, the inner radial surface having a different radial height than the outer radial surface; and a pocket recess opening at the tip and disposed between the inner radial surface and the outer radial surface.
 15. The blade of claim 14, wherein the inner radial surface and the outer radial surface extend from a leading edge to a trailing edge of the blade.
 16. The blade of claim 14, wherein a transition between the inner radial surface and the outer radial surface occurs along a camber line of the blade such that the outer radial surface has substantially a same thickness as the inner radial surface.
 17. The blade of claim 14, wherein a transition between the inner radial surface and the outer radial surface is asymmetric with respect to a camber line of the blade such that the outer radial surface has a different thickness than the inner radial surface.
 18. The blade of claim 14, wherein the pocket recess is asymmetric with respect to a camber line of the blade.
 19. The blade of claim 18, wherein the pocket recess is biased toward one of a suction side or a pressure side of the blade.
 20. The blade of claim 18, wherein the pocket recess is angled with respect to the camber line such that a first wall of the blade is thicker adjacent the leading edge than a second wall of the blade. 